How a big fan raises bigger questions about fire safety and energy conservation.
NFPA Journal®, September/October 2009
By Kathleen H. Almand, P.E., FSFPE
Energy conservation is driving new technology development in all aspects of our daily lives, from LED lighting in our homes to the batteries in our cars to the comfort control strategies in our workplaces. Many of these technologies, some of which are adapted from other uses, have a direct or indirect impact on fire safety—or at least require a closer look to determine what the impact might be.
One such technology is high-volume low-speed (HVLS) fans, which are being widely implemented as an energy-efficient means of providing a well-ventilated work environment in manufacturing and storage facilities and in many big-box stores. Originally invented by Walter Boyd in 1995 as a low-maintenance means of optimizing the productivity of dairy cattle, HVLS fans achieve their energy efficiency through the use of very large blades—up to 25 feet (8 meters) in diameter—that influence a correspondingly large volume of air.
Widespread use has prompted questions about the fans’ impact on the performance of ceiling-level sprinklers in manufacturing and storage facilities. Do the large fan blades obstruct the spray pattern of the sprinklers when the blades are stationary, or when moving? How do the air flows induced by these fans impact the effectiveness of sprinklers in controlling fires in these occupancies? Do the fans need to be shut off? When?
To answer these questions, the Fire Protection Research Foundation undertook a research program last year to develop design requirements for NFPA 13, Installation of Sprinkler Systems. The study, conducted by the San Diego office of Schirmer Engineering, was sponsored by, and built on previous studies by, the insurance and fan industries. Although the fans are in widespread use in many types of facilities, the research project of necessity focused on specific aspects of this broad issue: early suppression fast response (ESFR) sprinkler protection of Class A commodity in-rack storage. A study of fans on the market was undertaken to determine some worst-case scenarios for fan obstruction, and a series of small-scale studies of sprinkler spray pattern was conducted.
These studies concluded that the fans do not represent a significant obstruction to water flow if they are located three feet (0.9 meters) or more below the level of the sprinklers.
Two full-scale tests were then conducted to explore the impact of the air flows generated by the moving fan on sprinkler effectiveness in two scenarios varying the relative placement of fan and sprinkler head. These tests demonstrated that there are certain configurations in which sprinklers can continue to be effective in the presence of operating fans.
Questions remain, however, regarding the worst-case scenario for fan versus sprinkler placement, and extending the results to higher ceiling and storage heights and control mode sprinklers. The Foundation and its partners will work to answer these questions in future studies.
This project is an interesting example of how our rapid deployment of new technologies in response to our declining natural resources is affecting fire safety. The use of these fans is widespread, yet the questions about their interaction with sprinklers—and the formulation of practical strategies to address those questions—are playing catch-up. Sometimes, we don’t fully comprehend the impact of new technologies on fire safety until those technologies are in the marketplace.
There are many other examples where our interest in saving energy with new technologies—solar panels, “green” building materials, and so on—has a direct impact on fire safety. We can address that impact if we are ready for it. It is important for all of us in the fire safety community to keep up with developments in energy-saving technology, so that we can better ensure that the technology is fire-safe.
Kathleen H. Almand, P.E. , FSFPE, is the executive director of the Fire Protection Research Foundation.